Participation registration of co-authors

If co-authors of a paper want to participate at the conference and present the findings together with the main author, do they have to register as a participant (and pay)?

We recommend that every person attending the event registers as a participant in ConfTool, even if no registration fees are charged.

Overall, keeping all data in one system seems like a good idea to us.
This will make it easier for you to keep track who the attendants are.
Furthermore, as an example, there is a filtering function in ConfTool that allows you to send bulk e-mails to all presenters who are participants.